<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      margin: 0;
      padding: 0;
    }

    .outer {
      width: 200px;
      height: 200px;
      border: 1px solid black;
      margin: 100px auto;
      /* 开启3D空间 */
      transform-style: preserve-3d;
      /* 设置景深 （近大远小）*/
      perspective: 500px;
      /* 设置景深原点 */
      perspective-origin: 50px 50px;
    }

    .inner {
      width: 200px;
      height: 200px;
      background-color: rgba(117, 163, 209, 0.3);
      /* transform: rotateX(45deg); */
      transform: translateZ(-50px);
    }
  </style>
</head>

<body>
  <div class="outer">
    <div class="inner">11</div>
  </div>
</body>

</html>